prof:
I think you are making a mistake. Pizza is pretty clearly in the category discussed by the shulchan aruch in 168:17 regarding pashtida. The din of pashtida is that it is not pas kisnim at all, and one always makes hamotzi.
See beur halacha BD”H pashtida; There is a taz which says that a filling of meat or fish makes a food pas kisnim, and therefore only hamotzi when eaten in a shiur kvias seudah (I assume cheese has the same status). The beur halacha restricts this din to small pastries made as a snack, like pigs in a blanket.
Accordingly, pizza will be real pas, and will be hamotzi even when eaten in small amounts.
It bears noting here, that the din of “kovea seuda” as commonly referenced, is not completely correct. See mechaber 168:6, that one’s personal intentions are irrelevant, and the din is that if one eats the amount of kvias seuda, that is when one must make hamotzi. Therefore, even if one is eating cookies as a meal, if one eats less than the amount people normally eat as a meal, one must make mezonos.
The amount normally eaten as a meal is a machlokes. It is either 3-4 beitzim, or, the amount eaten at a seudas erev u’boker. MB 168:24